The present invention relates to gas generators, used to inflate air bags in a vehicle occupant protection system for example, and more particularly, to an improved dual chamber gas generator containing an improved structure for isolating the propellant chambers of a dual chamber inflator so as to ensure proper deployment of the airbag.
Inflation systems for deploying an air bag in a motor vehicle generally employ a single gas generator in fluid communication with an uninflated air bag. A firing circuit typically triggers the gas generator when the sensed vehicle acceleration exceeds a predetermined threshold value, as through the use of an acceleration-responsive inertial switch.
However, air bag inflation systems utilizing a single gas generator suffer from the disadvantage that the onset pressurization/inflation rate is generally set to provide aggressive initial inflation in order to achieve a particular inflation time related to occupant position. An aggressive onset rate of pressurization becomes problematic in situations where the occupant is out of position. More specifically, rapid onset pressurization of the air bag can cause the air bag to impact against the occupant with enough force to injure the occupant. The airbag volume and inflating capacity are designed to protect both large and small occupants and are generally not variable within the single gas generator. Occasionally, when an air bag utilizing a single gas generator is deployed, smaller occupants, usually children and smaller women, have been seriously injured.
Commonly owned U.S. Pat. No. 5,400,487 discloses an inflation system which overcomes the above problem by utilizing a plurality of gas generators which are controllably ignited to provide a variable inflation profile which can be tailored to any given occupant weight and/or position and for any crash type. While this arrangement dramatically improves the inflation system""s ability to protect an occupant, it does so at significant expense and complexity. The multiple gas generators and squibs add considerable cost to the system, while the firing control circuitry requires sophisticated processors capable of accurately timing the various ignition profiles.
Another proposal, as taught in commonly owned U.S. Pat. No. 5,934,705, is a gas generator having two chambers in a single housing defined by a mechanically retained wall between the ends thereof. Each housing is of a predetermined size that is determinative of the propellant capacity and consequently, of the inflating capability of each chamber. Upon the occurrence of a vehicle collision, depending on the weight of the passenger, either chamber or both may be selectively ignited thereby inflating the protective airbag. However, the structural integrity of such a known dual chamber inflator, may be compromised by failure of the wall separating the chambers when only one chamber is fired.
Given the above, typical dual chamber inflators often require a more robust design, resulting in relatively higher costs and more complicated manufacturing as compared to a single chamber inflator.
Therefore, a need exists for a dual chamber gas generator that exhibits a simplified design and therefore lower material and manufacturing costs, and yet can still produce selective air bag inflation pressurization without hazardous structural failure of the gas generator.
Complete isolation of the chambers of a dual chamber airbag inflator is critical to soft deployment of the airbag. Accordingly, the present invention relates to an improved structure for isolating the propellant chambers of a dual chamber inflator so as to insure proper deployment. Two separate igniter assemblies extend through primary and secondary propellant chambers for selective gas generation therein. A divider disc separates the primary and secondary chambers such that independent operation of each chamber is assured. The present invention permits sequential or simultaneous activation of the two chambers while enhancing the safety of the inflator and reducing the manufacturing costs.